1. Field of the Invention
The present invention relates to an upper tool for a press brake, and more specifically to an upper tool for a press brake which can be easily exchanged for the upper table. In more detail, it relates to an upper tool capable of operating an upper tool holder so as to increase a clamping force when the upper tool is attached to the upper tool holder.
2. Description of the Related Art
As is well known, a press brake is provided with an upper table (referred to as an upper apron, sometimes) and a lower table (referred to as a lower apron, sometimes) arranged in such a way as to be opposed to each other, and either of the upper or lower table is disposed movably in the vertical direction.
To bend a plate like workpiece for instance, an upper tool is mounted on the lower part of the upper table, and a lower tool is mounted on the upper part of tile lower table. Therefore, when the movable side table is moved up and down so that the upper and lower tools can be engaged with each other, a workpiece positioned between the upper and lower tools is to be bent.
Further, in the above-mentioned press brake, a number of upper tool holders are mounted on the lower part of the upper table to exchange the upper tool with an appropriate one according to the bending shape of the workpiece. In other words, the upper tools are supported by a number of upper holders so as to be exchanged.
In the prior art upper tool holder, the structure is such that an upper-tool pressing-down and fixing member is mounted on a holder body attached to the lower part of the upper table, and the upper-tool pressing-down and fixing member is fastened with fastening bolts to tightly fasten and fix the upper part of the upper tool between the holder body and the upper tool clamp.
Therefore, when the upper tool is required to be exchanged with another one, since a number of fastening bolts provided for a number of upper tool holders must be loosened, there exists a problem in that the exchanging work of the upper tool is extremely complicated and therefore troublesome.
To overcome the above-mentioned problem, a structure such that air cylinders are mounted on the upper tool holders to fasten and loosen the upper-tool pressing-down and fixing members has been developed.
In the above-mentioned structure, however, since an air cylinder must be provided for each of a number of the upper tool holders and additionally an air source is required, there raises another problem in that the structure is further complicated and therefore costly.
Further, in the prior art structure, there exists such an danger that when the pressing-down and fixing of the upper tool by means of the upper-tool pressing-down and fixing member is loosened, the upper tool drops. Further, when the upper tool is mounted on the upper tool holder, the upper-tool pressing-down and fixing member must be fastened tightly under the conditions that the upper-tool pressing-down and fixing member is fastened slightly to such an extent that the upper tool will not drop and thereafter the upper and lower tools are aligned with respect to each other, thus causing a problem in that the upper tool exchanging work is troublesome.
Additionally, E.P. Pat. No. 0387121A1 discloses a tool in connection with the present upper tool. In this prior art, an upper tool is fastened with a holder body through an upper-tool clamping member pivotably mounted to an upper table of a press brake. The detachment and attachment of the upper tool are attained by rotating the clamping member so as to avoid a pivot axis about which the member is pivoted. Therefore, an operation that an operator rotates the upper tool, supporting an molding die of 20.about.30 kg in weight by his hand, is extremely dangerous for his waist and hands.
Furthermore, in case of arranging a plurality of upper tools in order along the longitudinal direction in the upper tool holder, there is caused a problem that it is impossible to attach a sequent upper tool to the upper-tool clamping member in which the other upper tool has already clamped, in the longitudinal direction of the upper tool.